Ultra-wide band frequency offset estimation systems and methods for analog coherent receivers

Abstract

Described herein are systems and methods that allow for correcting a residual frequency offset in the GHz frequency range by using low-complexity analog circuit implementations of a broad-band frequency detector that comprises two analog polyphase filters in a dual configuration. Each filter comprises an RC network of cross-coupled capacitors that facilitate filters with opposite passbands and opposite stop-bands. In various embodiments, the outputs of the two filters are combined to obtain power metrics that when subtracted from each other, deliver a measure of the imbalance between the positive and negative halves of a frequency spectrum. Since the measure is substantially proportional to a frequency offset within a linear range spanning 5 GHz or more, the polyphase filters may be used in a broad-band frequency detector that, based on the measure, adjusts the frequency offset.

What is claimed is: 
     
       1. A method for estimating a frequency offset in a broad-band, zero-IF receiver system that has in-phase and quadrature receiver branches, the method comprising:
 determining a first power metric by using a first output of a first polyphase filter that is coupled to in-phase (I) and quadrature (Q) branches of a receiver and that is more responsive to signal power at frequencies in a positive half of a signal spectrum than frequencies in a negative half of the frequency spectrum; 
 determining a second power metric by using a second output of a second polyphase filter that is coupled to the I and Q branches and that is more responsive to signal power at frequencies in the negative half than to frequencies in the positive half of the frequency spectrum; 
 using the first and second power metrics to obtain a measure of an imbalance between the signal power in the positive and negative halves of the frequency spectrum; and 
 using the measure to determine at least one of a magnitude of a frequency offset or a sign of a frequency offset. 
 
     
     
       2. The method according to  claim 1 , further comprising using the measure to adjust the frequency offset. 
     
     
       3. The method according to  claim 1 , wherein the first and second polyphase filters comprise a passive RC network that comprises capacitors and resistors. 
     
     
       4. The method according to  claim 3 , further comprising cross-coupling the capacitors and resistors between in-phase and quadrature branches of a receiver. 
     
     
       5. The method according to  claim 1 , wherein the first and second polyphase filters are configured as coarse frequency detectors. 
     
     
       6. The method according to  claim 5 , further comprising summing an output of one or more fine frequency detectors with outputs of a coarse frequency detector. 
     
     
       7. The method according to  claim 6 , further comprising adjusting a gain such that the one or more fine frequency detectors dominate over the output of the coarse frequency detector. 
     
     
       8. The method according to  claim 1 , wherein the first and second power metrics are obtained by steps comprising squaring respective outputs of the first and second polyphase filters to determine which filter outputs a greater signal. 
     
     
       9. A broad-band frequency detector for estimating a frequency offset, the broad-band frequency detector comprising:
 a first polyphase filter that receives a modulated input signal and determines a first power metric, the first polyphase filter having greater gain at positive frequencies than at negative frequencies; 
 a second polyphase filter that that receives the modulated input signal and determines a second power metric, the second polyphase filter having greater gain at negative frequencies than at positive frequencies; and 
 a comparator circuit that uses the first and second power metrics to obtain a measure of an imbalance between positive and negative halves of a frequency spectrum, the measure being substantially proportional to a frequency offset, the broad-band frequency detector uses the measure to adjust the frequency offset. 
 
     
     
       10. The broad-band frequency detector according to  claim 9 , wherein the first and second polyphase filters have passbands that are substantially mirrored with respect to each other around a DC value. 
     
     
       11. The broad-band frequency detector according to  claim 9 , wherein the first and second polyphase filters have stopbands that are substantially mirrored with respect to each other around a DC value. 
     
     
       12. The broad-band frequency detector according to  claim 9 , wherein the first and second power metrics are obtained by steps comprising squaring respective outputs of the first and second polyphase filters. 
     
     
       13. The broad-band frequency detector according to  claim 12 , wherein each of the first and second polyphase filters comprises a passive polyphase RC network. 
     
     
       14. The broad-band frequency detector according to  claim 13 , wherein the passive polyphase RC network comprises one or more adjustable circuit components. 
     
     
       15. The broad-band frequency detector according to  claim 13 , wherein the passive polyphase RC network for the first polyphase filter comprises capacitors and resistors that are cross-coupled between in-phase and quadrature branches of a receiver.